Process for the recovery of antimony pentachloride from catalyst solutions

ABSTRACT

The invention relates to the recovery of antimony pentachloride from catalyst solutions, which are used for the fluorination of chlorosubstituted methanes or ethanes. The process is based on the reduction of antimony pentachloride, which is dissolved in a used catalyst solution by means of trichloroethylene, at a temperature of from 100* C to 170* C. The crystalline antimony trichloride obtained precipitates from the solution and is separated from all the impurities. The antimony trichloride obtained can be re-oxidized to form antimony pentachloride by any known process.

United States Patent 1 Field of Search 423/491, 87

Ertel et al. 1 Sept. 18, 1973 PROCESS FOR THE RECOVERY OF [56] References Cited ANTIMONY PENTACHLORIDE FROM UNITED STATES PATENTS CATALYST SOLUTIONS 2,102,737 12/1937 Peck et a1. 423/491 Inventors; Ha -"nut Ertel Hofheim/Taunus; 2,786,738 3/1957 Ruh Cl ai. 423/87 Peter Frisch, Schwalheim, both of Germany Primary Examiner-Edward Stern [73] Assignee: Farbwerke l-loechst Attorney-Henry Koster Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt/Main, v [57] ABSTRACT Germany I The invention relates to the recovery of antimony pentachloride from catalyst solutions, which are used for [22] Filed' 1971 the fluorination of chlorosubstituted methanes or eth- [2i] Appl. No.: 199,308 anes. The process is based on the reduction of anti- I mony p'entachloride, which is dissolved in a used catalyst solution by means of trichloroethylene, at a tem- [30] Foreign Application Priority Data perature of from 100C to i70 C. The crystalline anti- 18, c' lf' P 20 56 mony trichloride obtained precipitates from the solution and is separated from all the impurities. The anti- US. Cl. 423/87, 423/491 mony "ichloride Obtained can be moxidized to form Ill. i y pentachloride y known process l Claim, No Drawings PROCESS FOR THE RECOVERY OF ANTIMONY PENTACHLORIDE FROM CATALYST SOLUTIONS The present invention relates to a process for the recovery of antimony pentachloride from catalyst solutions. 1

Antimony pentachloride serves as catalyst for the reaction of chlorinated hydrocarbons with hydrogen fluoride, in which process one or several chlorine atoms are exchanged for fluorine. According to this method, chloro-fluoro-hydrocarbons are prepared technically.

1n the course of the continuous or discontinuous performance of this process, for example, in the case of the preparation of Cl-lClF, from chloroform or of CCl -,F and/or CCI F from carbon tetrachloride, organic impurities having an elevated boiling point are accumulated in the liquid catalyst. These impurities are not,'or not to a sufficient degree, discharged together with the desired reaction products. This leads to a dilution of the catalyst and reduces its efficiency. Renewal becomes necessary, when its activity has become too low.

The working-up of the used catalyst solutions by distillation wouldobviously solve the problem but it is rather complicated. The used catalyst solutions contain only an insignificant amount of Sb-F-compounds in the presence of excess carbon tetrachloride or chloroform. During distillation, however, temperatures are required at ,which the SbCl, present in the used contact solutions has already a rather high vapour pressure and thermally decomposes to yield chlorine, which is highly corrosive to the steel normally used as material for the reaction vessel. Moreover, some of the impurities have a high melting point, so that there is also the risk of blocking up the distillation apparatus.

The present invention provides a simple process for the recovery of antimony pentachloride from these catalyst solutions, which comprises heating the catalyst solution with trichlorethylene at a temperature of from 100 to 170 C, preferably from 110 to 130 C, in which process all the antimony is virtually converted into antimony trichloride, which is separated in a crystalline form from the organic solution and is then worked up to form antimony pentachloride.

Antimonytrichloride may be worked-up, for example, by chlorination with elementary chlorine.

The antimony pentachloride thus obtained can readily be used again for a fluorination process. The separated organic solution, which contains only a small amount of antimony compounds, may either be decomposed as such' into its components according to com mon methods by fractional distillation, or the antimony compounds are separated by washing the organicsolution with, for example, hydrochloric acid.

The reaction of the antimony (V) compounds'with tri-chlorethylene is generally carried out in a nickel autoclave, under a moderate pressure, as it corresponds to the vapour pressure of the solution at the selected temperature. The used catalyst solution and the trichlorethylene required are combined in the autoclave and are heated to the reaction temperature of from 100 to 170 C, preferably from 110 to 130 C. The reaction time is in the range of from 1.5 to 150 hours, depending on the reaction temperature. Even in the case of an incomplete reduction, at least part of the antimony used can be separated or obtained as antimony trichloride. It is also possible to operate without pressure, ifa component increasing the boiling point is added to the reaction solution, for example, perchlorethylene.

The amount of trichlorethylene required per mole of antimony (V) compound is in the range of from 1 to 3 moles, preferably from 1.5 to 2.5 moles. The upper limit is not crucial, as antimony trichloride is only slightly soluble in trichlorethylene. Owing to the low vapour pressure of the dissolved antimony trichloride, the fractional distillation of the separated organic mixture is disturbed only to a very limited extent. The carhon-containing compounds obtained during the fractional distillation contain chlorine and fluorine and are in particular compounds containing 1 or 2 carbon atoms. This fraction can be used in further fluorination processes according to known methods.

The use of other olefins as chlorine acceptors does not have the same result, since they do not, or not only, react by adding chlorine the less chlorine they contain but yield tarry products in side reactions. If perchlorethylene is used as chlorine acceptor, hexachlorethane is obtained, which is .moderately soluble in other halogen hydrocarbons and which tends to sublime, and furthermore dissociates partially into perchlorethylene and chlorine at the reaction temperature.

In view of the scarcity of antimony and the tremendous difficulty to recover antimony from waste material, the claimed process represents a significant technical progress.

The following Examples serve to illustrate the invention.

EXAMPLEI:

1 Liter of used catalyst solution consisting mainly of SbCl CC 1 CCl F and ethane derivatives containing fluorine and chlorine had a weight of 2.17 kg and contained, according to an analysis, 672 g of Sb, which corresponded to 5.52 gramatoms.

These 2.17 kg of catalyst solution were heated in a nickel autoclave having a capacity of 4 liters, together with 1 liter of trichlorethylene, for 24 hours at a temperature of 120 C, under reflux. Subsequently, the solution was cooled to room temperature.

The SbC l precipitates in the form of coarse crystals at the autoclave wall. It was filtered off with suction and was washed three times with 300 milliliters each of CCl,,; after having been dried in a desiccator, it had a weight of 1.20 kg. According to an analysis, this product contained 593 g of Sb corresponding to 4.88 gramatoms, i.e. 1,115 g of SbCl The product thus contained 93 percent of SbCl and was therefore to be considered as technically pure. 88.5 percent of the an- EXAMPLE2:

1 Liter of the used catalyst solution as described in Example 1, which contained 5.52 gram-atoms of antimony as antimony halides, was refluxed together with 800 g of trichlorethylene (6.1 moles) and 2 liters of perchlorethylene for 150 hours in a glass recipient. During this process a liquid temperature in the range of from 1 10 to 120 C was found. 'When the solution was cooled, the SbC l precipitated in the form of colourless crystals. The dark-coloured solution was decanted. The crystalline antimony trichloride had a weight of 1,322 g. It contained 1,203 g of SbCl which corresponded to a yield of percent of the antimony used.

What is claimed is:

temperature in the range of to C under superatmospheric pressure or by further addition of perchloroethylene under atmospheric pressure; separating the crystalline antimony trichloride precipitated from the organic solution; and converting said antimony trichloride to antimony pentachloride.

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